Many techniques for gear diagnostics are based on the analysis of mechanical vibrations measured from a gearbox. The target is to detect the presence of possible faults at an early stage of development and to monitor the evolution of the faults, in order to estimate the residual life of the gearbox and/or choose an adequate plan of maintenance. The monitoring is typically based on converting the signal that represents the mechanical vibrations measured from the gearbox into the frequency domain and subsequently searching from the resulting spectrum of mechanical vibrations indications of faults. For example, publication DE19933105 discloses a method wherein an indication of a defective gear is provided when a measured spectrum deviates from a reference spectrum. The gearbox to be monitored can be, for example but not necessarily, a gearbox of a wind power station.
A monitoring arrangement comprises typically vibration sensors attached to the gearboxes to be monitored, data communications connections from the vibration sensors to a centralized monitoring station, and, in the monitoring station, processing and display equipment for processing the measured data and for displaying the spectrums of mechanical vibrations to operators who have been trained to analyze the spectrums. The monitoring arrangement may cover hundreds or even a thousand gearboxes to be monitored, and for example 20 spectrums can be measured from each gearbox per day. This would mean that even 20000 measured spectrums are to be analyzed per day. Thus, there is a clear need for methods and systems which are suitable for automated analysis and/or for pre-pruning of the measured results so as to reduce the required amount of human labor.